Question on MA-15D's

Hi - I have a pair of Edirol MA-15D micro monitors. My home studio as just an average size bedroom. These look sharp but I am not sure about the quality of the sound...anyway my main question is, for playback should the bass and treble knobs be in their center position, or set all the way down - to a truer indication of what my mix sounds like?  I am also wondering when I should use the digital line in volume, versus the rca /anologue line volume?  
 
Thanks !